Energy Savings Estimates for Occupancy- and Temperature-based Smart Ventilation Control Approaches in Single-family California Homes

As homes become more air-tight in response to energy efficiency concerns and changes in building codes, new ventilation solutions are needed in order to provide for a healthy indoor environment while minimizing energy use.  This is especially true in the state of California, whose 2019 Title 24 Standard encourages tight envelopes through prescriptive air sealing and performance requirements, and requires whole-house mechanical ventilation in all new homes.  One such solution employs a real-time assessment of the indoor environment and dynamic operation of a ventilation system.  In this study, we investigated the energy savings benefits and indoor air quality improvement available with such a "smart" control strategy for ventilation in four very different California climate zones. We simulated annual operation of multiple control strategies on detailed models of two representative Title 24-compliant prototype homes in California.  We did this through co-simulation of the EnergyPlus building energy software and CONTAM, an airflow and indoor air quality simulation software, and an automated Python-based parametric analysis of control variables.  All simulations employed the assumption of a single well-mixed zone and the equivalent ventilation method outlined in ASHRAE Standard 62.2-2016.  Results show several interesting trends which we hope will help inform standards-development teams, home builders, consumers, and smart ventilation equipment manufacturers in their approach to dealing with dynamically controlled ventilation.  In general, control strategies which included optimization based on sensing of outdoor air temperature vastly outperformed strategies which did not.  Among these, a temperature cutoff strategy performed nearly as well as more complex variable airflow and variable-exposure-target strategies.  Control strategies based solely on occupancy were among the worst performing.  Other issues require more investigation such as the acceptability of a seasonal shifting strategy over a daily shifting strategy, and the use of a maximum exposure limit.  This work serves as the foundation for ongoing work on multi-zone control and control based on individual pollutant measurements.